Photonic devices such as waveguides, modulators, detectors, demodulators, resonators, taps, splitters, amplifiers, gratings, couplers, and others, have been successfully integrated on an integrated circuit substrate. Typically, photonic devices have a waveguide core material for channeling light and a cladding surrounding the core for confining the light in the core. Often the substrate is formed of silicon and the core material is formed of polysilicon. When such devices are fabricated on a substrate there must also be a decoupling of the light passing through the core from being coupled to the substrate to prevent optical signal loss. This requires a suitable optical decoupler between the core and substrate. Often a silicon on insulator (SOI) substrate, having an optical insulator in the form of a silicon dioxide layer beneath a silicon upper layer can be used for this purpose. Alternatively, a bare silicon substrate can be provided with an overlying optical decoupler, for example, a silicon dioxide layer, on which photonics devices having a waveguide core can be built. In addition, the current trend is to integrate electronic circuits, and devices on a substrate together with photonics circuits and devices. This presents additional problems as a substrate having suitable optical isolation used for photonics devices and circuits may be unsuitable for desired operating characteristics for electronic devices and circuits fabricated on the same substrate.
An efficient technique and structure for optically isolating photonics circuits and devices from a substrate, while providing a suitable cladding layer and low signal loss, and allowing for ease of integration of electronic circuits and devices on the same substrate is desired.